Conventionally, a functional adhesive sheet has been applied to an assembly of various kinds of optical equipments, electric equipments or electronic equipments (including parts). Among them, in view of productivity, adhesive sheets adaptable to rework (that is, re-lamination work by peeling from an adherend (a liquid crystal display apparatus or a protection panel or the like) for repairing or the like, and it may also be referred to as repair) of a lamination article have been required, in particular, in lamination with a liquid crystal display apparatus having high price parts (hereafter it may also be referred to as LCD), adhesive sheets adaptable to rework have been required strongly.
On the other hand, securing of adhesion with the adherend has also been required, however, because adhesion and rework property are conflicting characteristics, satisfaction of both has been difficult.
In addition, in recent years, in view of practical reliability of the assembly parts where a functional adhesive sheet and the adherend are laminated, the functional adhesive sheets having higher adhesion (tackiness) have been required, wherein (1) securing of high adhesion enough to clear a point pressurization test, to confirm generation of peeling of the functional adhesive sheets or air bubbles, by adding point load, using a pressurization element, from the surface of the assembly product (for example, a laminated body of LCD/the functional adhesive sheets/a protection panel), on the other hand, results in significant decrease in (2) securing of workability by maintaining light peeling property of a releasing protection sheet present at the surface of the functional adhesive sheets in the assembly, and (3) adhesion gap or rework property in repair or exchange of parts. Accordingly, satisfaction of both adhesion and rework property has been still more difficult.
Under the above situation, various proposals have been made conventionally, as technology for improving or solving the problem of the above (1).
That is, (i) in view of enhancement of adhesion, there have been proposed various technologies for enhancing the adhesion with a substrate, by performing UV-ray treatment onto a pressure sensitive adhesive layer of an adhesive sheet (for example, refer to PATENT DOCUMENTS 1 to 3).
For example, in PATENT LITERATURE 2, there has been disclosed a production method of an adhesive sheet superior in bonding force between the substrate and the adhesive layer, wherein the surface of various known adhesive layers to be bonded with the substrate is subjected to activation treatment such as corona discharge treatment, plasma treatment, UV-ray treatment, and in the case of UV-ray treatment, it is irradiated with an energy of 10 mJ/cm or higher, also, in the case of corona treatment, a surface wetting index of an additive-free polyethylene film is treated at 34 dyn/cm or higher, preferably 40 dyn/cm or higher.
However, depending on the material of a pressure sensitive adhesive, enhancement effect or stability of adhesion by UV-ray treatment thereof or the like differs, and it is not an almighty method. In particular, as for a silicone-based pressure sensitive adhesive attracted the attention as an optical material superior in transparency or heat resistance, because of having such characteristics specific to silicone that the silicone surface hydrophilized by surface activation treatment becomes hydrophobic quickly, surface treatment effect is deactivated in a short period of time, and thus enhancement of adhesion by surface activation treatment has been said to be difficult (for example, refer to NON PATENT LITERATURE 1).
This hydrophobic recovery, which means quick return to hydrophobic property, is generated by diffusion of low molecular weight siloxane from inside to the surface, or by coming out of a methyl group component, whose concentration was decreased by generation of a hydrophilic group at the surface, to the surface by re-orientation caused by molecular motion, usually, it returns to an original hydrophobic state, for example, within about 24 hours after plasma treatment. Accordingly, although various challenges have been performed to suppress hydrophobic recovery and to achieve the maintenance of stable hydrophilic property, an essential solution has not been attained at present.
In addition, (ii) in an adhesion film for surface protection, a method for satisfying both rework property and adhesion, by performing UV-ray treatment or the like onto an adhesive layer, has also been proposed (for example, refer to PATENT LITERATUREs 4 and 5).
However, the above adhesion film for surface protection is not the one for adhering firmly with the adherend, in view of use purpose thereof, and is difficult to secure adhesion which can satisfy the above point pressurization test, and thus is not the one for applying technology of a surface protection film or the like to the functional adhesive sheet.
Still more, (iii) the present applicants have also proposed a silicone-based adhesive sheet which satisfies both rework property and adhesion (refer to PATENT LITERATURE 6), however, in view of securing adhesion in a degree of passing the above point pressurization test, it has still room for improvement, in particular, in low-hardness silicone gel, securing of adhesion is difficult, and technological hurdle to enhance the adhesion thereof is high.
In addition, (iv) as a means for making satisfied both adhesion in a degree of passing the above point pressurization test and rework property, such a means is said effective that initially provides low tackiness enabling to rework to an adherend, and after lamination increases the adherence force with time, and for example, there has been proposed a pressure adhesive agent modified with a functional group in which the surface of the pressure adhesive agent exhibits adhesion reactivity by an interface contact reaction, and an adhesive sheet provided with pressure adhesive agent thereof (for example, refer to PATENT LITERATURE 7).
However, the above means and methods need optimization of the functional group exhibiting adhesion reactivity by each adherend, and thus have a problem of requiring a lot of labor.
As described above, although technology and means (techniques) of the above (i) to (iv) have been proposed as technology to improve or solve the problem, they are not sufficient as technical idea to solve the above (1) securing of adhesion, (2) workability by maintaining light peeling property or (3) rework property, and the transparent adhesive sheet for optics which is capable of satisfying both securing of adhesion, which can pass the above point pressurization test, and rework property has earnestly been desired.